That's not cheating, that's spending a ton of diamonds. He aided guildies and/or friends to get a piece of each great building blueprint, then bought the rest with diamonds, bought the goods with diamonds and possibly bought the forge points with diamonds. Of course this guy could have started that city a LONG time ago and did it the excruciatingly hard way, by getting all those blueprints from just aiding, and bought the goods with forge points.